Frequency-doubling sonic transducer



Feb. 14, 1967 R. M. HAKNES ETAL FREQUENCY-DOUBLING SONI C TRANSDUCER Filed Feb. 5, 1964 tmQmQumt t0 mmllms m m 053 S.

INVENTORS. ROBERT M. HAINES THOMAS W. MARTINEK DONALD LKLASS United States Patent 3,304,378 FREQUENCY-DOUBLING SONIC TRANSDUCER Robert M. Haines and Thomas W. Martineh, Crystal Lake, and Donald L. Klass, Harrington, llL, assignors, by mesne assignments, to Union Oii Company of California, Los Angeles, Calif., a corporation of California Filed Feb. 3, 1964, Ser. No. 342,154 9 Claims. (Cl. 179-433) This invention relates to audio frequency doubling devices.

A number of electrical phenomena are exhibited when certain suspensions of solids or liquids in oils are subjected to shear stresses. When a film of a suspension of nonconducting particles in an oleaginous vehicle of relatively low dielectric constant, such as a dispersion of silica in a mineral oil, is subjected to shear stress, as between opposing electrically conductive surfaces of two bodies moving with respect to each other, the film exhibits changes in electrical properties, such as a decrease in DC. resistance, a change in dielectric constant, and the generation of an induced potential. The magnitude of each of these phenomena depends on the fluid composition, the shear rate, the fluid temperature, and the spacing between the opposing surfaces, and in addition, the magnitude of the induced potential depends on the compositions of the opposing surfaces. For the purpose of this application, such suspensions are hereinafter designated shear-responsive or electrodynamic fiuids.

The audio frequency doubling device of the invention utilizes shearresponsive fluids to double the frequency of an audio signal. These devices are especially useful in lieu of conventional microphones in machines for recording and reproducing spoken words, as for transcription by a stenographer, such as those sold under the trademark of Dictaphone and similar devices. Devices such as Dictaphones, tape recorders, and the like, which are used by stenographers to transcribe the spoken word into typed copy, generally can be played back at a speed somewhat less than the recording speed to facilitate the transcription. However, the playback of the recording device at lower speeds results in a loss of intelligibility of the reproduced audio signal, thereby making the reproduced audio signal at least partially unintelligible. The audio frequency doubling device of this invention is superior to conventional microphones in such recorders in that the utilization thereof will produce intelligible audio reproduction when the playback speed is a fraction, e.g., one-half, the recording rate.

Briefly, the audio frequency doubling device comprises two spaced bodies having opposing, spaced, electrically conductive surfaces between which a shear-responsive fluid is confined, with one of the bodies being movable with respect to the other. The movable body is connected by a substantially incompressible mechanical coupling to a vibratory diaphragm so that vibratory motion of the diaphragm will result in vibratory movement of the movable body with respect to the other body. Each of the two electrically conductive surfaces is electrically connected by a lead wire to suitable means for converting fluctuating direct current voltage values into alternating current voltage values, such as to an audio transformer. One of the lead wires contains a DC. potential source so that the shearing of the shear-responsive fluid caused by the vibratory movement of the movable body with respect to the other body results in a change in the resistance of the shear-responsive fluid to increase or decrease the DC. voltage applied across the primary winding of the transformer and correspondingly to increase or decrease the current flow through the transformer as a function of the applied vibratory motion. This shearing of the shearresponsive fluid occurs twice for each single audio cycle 3,304,378 Patented Feb. 14, 1967 applied to the diaphragm so that the audio output of the transformer is twice the frequency of the audio input of the diaphragm. The output of the transformer may be amplified or may be utilized directly. When the output of the transformer is fed into a recorder, the recorded message can be played back at a fraction, e.g., one-half, of the recording speed, and intelligible reproduction obtained.

It is, therefore, the primary object of this invention to provide a device for increasing the frequency of an audio signal. Another object of this invention is to provide an audio frequency doubling device utilizing a dispersion of non-conducting particles, either solid or liquid, in an 'oleaginous vehicle of low dielectric constant. Still another object of this invention is to provide a device which is useful in lieu of conventional microphones in machines used to transcribe a spoken message into printed copy. These and further objects of this invention will become apparent or will be described as the description thereof herein proceeds and reference is made to the accompanying drawing which is an elevational view, partly in section and partly schematic, of the audio frequency doubling device of this invention.

The audio frequency doubling device of this invention is best described in relation to the accompanying drawing, wherein the reference numeral 19 designates a suitable case which is formed of a suitable electrically insulating material, such as a phenol-formaldehyde resin, with bellshaped end 12. Case 10 is formed with internal shoulder 14 in bell-shaped end 12 and wall 16 intermediate the ends thereof. Perforated cover 18 is secured to bellshaped end 12 by threads 20. Held in place between shoulder 14- and cover 18 by annular rubber gaskets 22 is vibratory diaphragm 24. No criticality is claimed as to the construction of diaphragm 24 and it may take the form of vibratory diaphragms found in conventional microphones. Diaphragm 24 is preferably formed so that it has a diameter slightly less than the interior diameter of the portion of bell-shaped end 12 in which it is disposed.

Adjacent to the end of case 10 opposite bell-shaped end 12 is electrically conductive plate 26 which is held in place by threads 28 to form chamber 30. The surfaces of case It and wall 16 within chamber 30 are provided with electrically conductive liner 32 which is in electrically conductive relationship with plate 26 when plate 26 is secured in place. Disposed within chamber 30 is electrically conductive, movable member 34 having an outer surface spaced from but substantially conforming to the shape of chamber 30. Chamber 30 and member 34 may have a variety of cross-sectional areas, such as circular, rectangular, octagonal, etc, and, in fact, member 34 may be a substantially fiat, ribbon-like member provided chamer 30 is of a suitable shape. A shear-responsive fluid is disposed in the space between movable member 34 and the walls of chamber 30. Spacings of about 0.003 to 0.030 inch are generally suitable, although other spacings may be used.

Movable member 34 is supported at one end of electrically conductive rod 38 extending through soft rubber sealing plug at} in a central opening in wall 16. The other end of rod 33 is fastened to diaphragm 24. Sealing plug 49 serves to confine the shear-responsive fluid within chamber 39 while permitting rod 38 to impart vibratory motion to member 34 from diaphragm 24. If desired, movable member 34 may be maintained spaced from the walls of chamber 3t by a non-conducting rod projecting from member 34 and movably supported within a hollow in plate Z, or by non-conducting springs extending between mcmber 34 and the walls of chamber 30.

Electrically connected to plate 26 and rod 38 are lead wires 42 and 44, respectively, which pass through opening 46 in end cover 48. End cover 48 is secured to case 10 by threads 50. Conductor 4'2 and conductor 44, which includes potential source 52, are connected to primary winding 54 of transformer 56. Secondary winding 53 of transformer 56 may be connected to an audio amplifier or recorder.

In operation, when one using the audio frequency doubling device of this invention speaks into bell-shaped end 12 of case 10, vibratory motion will be imparted to diaphragm 24. The vibratory motion of diaphragm 24 will be transmitted through rod 38 to vibrate member 34 with respect to the walls of chamber 30, thereby to shear the fluid confined within chamber 30. The shearing of the shear-responsive fluid in response to the vibratory motion of diaphragm 24 results in a reduction of the DC. resistance of the shear-responsive fluid to increase the current applied by potential source 52 through conductors 42 and 4440 primary coil 54 of transformer 56. Inasmuch as the shearing of the mechanofluid occurs twice for each single audio cycle applied to diaphragm 24, the audio output derived from secondary winding 58 of transformer 56 Will be twice the audio frequency input to diaphragm 24.

Although the apparatus of this invention has been described in relation to a specific embodiment, it will be apparent that obvious modifications may be made by one skilled in the art without departing from the intended scope of this invention. As for example, the device may be constructed so that a chamber having an electrically conductive interior surface is movable with respect to a second member which is disposed within the chamber and has an electrically conductive outer surface spaced from the walls of the movable member. It will be evident that it is essential that the opposing electrically conductive surfaces of the two members which are movable with respect to each other he maintained in electrically insulating relationship excluding the external electrical circuit, as represented by lead wires 42. and 44, potential source 52 and primary winding 54 in the accompanying drawing.

The shear-responsive compositions utilized in the apparatus and method of this invention form no part of the invention, and, for the purpose of this specification and claims, the terms liquid and fluid are intended to include liquids and fluids in the ordinary sense of the terms, i.e., readily flowing compositions and compositions of relatively high viscosity, i.e., those having a grease-like consistency at room temperature. In general, the shear-responsive compositions will consist of at least about 1% by volume and preferably 5 to 48% by volume of particulate poorly-conducting materials dispersed in a non-polar oleaginous vehicle, which is weakly absorbed by the particulate material and has a dielectric constant less than about 5. The poorly-conducting particles, which may be either of piezoelectric or non-piezoelectric materials, have an average size in the range of about 0.001 to 5.0 microns diameter, preferably about 0.01 to 1.00 micron diameter. Finely divided silica (a non-piezoelectric material) is especially useful for use in shear-responsive fluids. Examples of other poorly-conducting particles which may be used include aluminum octoate, aluminum oleate, aluminum stearate, barium titanate, calcium stearate, activated charcoal, crystalline D-sor'bitol, lead oxide, lithium stearate, magnesium silicate, micronized mica, white bentonite, and zinc stearate, vanadium pentoxide, basic aluminum acetate, etc.

The oleaginous vehicle in which the poorly-conducting particles are dispersed is preferably a refined mineral oil fraction having a viscosity within the range of about 50 to 300 SUS at 100 F., and an initial boiling point greater than about 500 F. However, a wide variety of non-polar oleaginous materials which are weakly adsorbed by the non-conducting particles can be employed. The vehicle can be considered to be only weakly adsorbed when it is less strongly absorbed by the particles than are the other constituents. Examples of suitable materials include white oils, lubricating oil stocks such as 80 vis. neutral oil, transformer oils, synthetic oils resulting from polymerization of unsaturated hydrocarbons, alpha methyl benzyl ether, benzene, bromocyclohexane, chlorinated paraffin, di-benzyl ether, dichloroethyl ether, chlorinated or fluorinated hydrocarbons in the lubricating-oil viscosity range, N-butyl ether, silicate ester, toluene, tributyl phosphate, etc.

Where volumes of the non-conducting particles in the high concentrations are incorporated in the shear-responsive liquid, it is usually necessary to add a material to fiuidize the mixture and keep the viscosity of the shearresponsive liquid at a reasonable level. For this purpose, varying amounts of a neutral surfactant can be incorporated to maintain the mixture of silica and vehicle as a fluid. Suitable neutral surfactants which may be used are selected from the polyoxyalkylene ethers, hydroxyethers, polyhydroxy-ethers and esters, as Well as neutral sulfonates and other neutral surfactants. Other neutral polar organic materials such as C C monoor polyhydric alcohols are suitable fluidizers. Suitable neutral fluidizers include glycerol monooleate, sorbitan sesquioleate, glycol monooleate, alkyl aryl polyether alcohols, sodium dialkylsulfosuccinate, hexyl ether alcohol, butyl Cellosolve, octyl alcohol and dodecyl alcohol. The neutral fluidizer may be added in quantities suflicient to fluidize the mixture of vehicle and particles but usually no more than is necessary to obtain sufficient fluidity is used. The amount added will seldom exceed about 25% by volume.

A variety of polar materials, including water, may be used to alter the properties of the shear-responsive liquid. Lower hydroxy-substituted hydrocarbons have been found to be highly efficient. Especially preferred are the aliphatic polyhydroxy-substituted hydro-carbons such as ethylene glycol. In general, activating material in the range of about 0 to 10% by volume will be added to the shear-responsive liquid.

The following readily flowing, shear-responsive liquid is set forth only as an example of one suitable fluid which may be utilized.

Wt. percent Silica 48.48 Water (adsorbed on the silica) 6.18 Glycerol monooleate 17.75 vis. neutral oil 27.59

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. An audio frequency doubling device comprising first and second spaced members having opposing elec trically conductive surfaces, one of said members being movable, a shear-responsive fluid confined between said surfaces, a vibratory diaphragm mechanically connected to the movable member in such manner that the vibration of said diaphragm imparts vibratory movement to the movable member, and electrical conductor means connected to each of said first and second members.

2. An audio frequency doubling device in accordance with claim 1 in which said first member is a hollow member having an electrically conductive interior surface, and said second member has an electrically conductive exterior surface and is disposed within said first member.

3. An audio frequency doubling device in accordance with claim 2 in which the outer surface of said second member substantially conforms to the shape of the inner surface of said first member.

4. An audio frequency doubling device in accordance with claim 3 in which said second member is connected to said diaphragm.

5. An audio frequency doubling device in accordance with claim 4 in which a rigid rod extends from said diaphragm to said second member.

6. An audio frequency doubling device in accordance with claim 5 in which the opposing surfaces of said first to the movable member in such manner that vibration of said diaphragm imparts vibratory movement to the movable member, electrical conductor means connecting said first and second members in series with a source of direct current and means for converting fluctuating direct current produced by vibratory movement of said movable member into detectable alternating current signals.

No references cited.

KATHLEEN H. CLAFFY, Primary Examiner.

F. N. CARTEN, Assistant Examiner. 

1. AN AUDIO FREQUENCY DOUBLING DEVICE COMPRISING FIRST AND SECOND SPACED MEMBERS HAVING OPPOSING ELECTRICALLY CONDUCTIVE SURFACES, ONE OF SAID MEMBERS BEING MOVABLE, A SHEAR-RESPONSIVE FLUID CONFINED BETWEEN SAID SURFACES, A VIBRATORY DIAPHRAGM MECHANICALLY CONNECTED TO THE MOVABLE MEMBER IN SUCH MANNER THAT THE VIBRATION OF SAID DIAPHRAGM IMPARTS VIBRATORY MOVEMENT TO THE MOVABLE MEMBER, AND ELECTRICAL CONDUCTOR MEANS CONNECTED TO EACH OF SAID FIRST AND SECOND MEMBERS. 